Current visible imaging technology is mostly based on Charge Couple Device (CCD) structures. CCDs are based on a Metal Oxide Semiconductor (MOS) technology where charge is transferred from one capacitive well to another thus requiring large capacitances and power. Complementary Metal Oxide Semiconductor (CMOS) imagers are a viable alternative to CCDs. CMOS technology is currently used in almost all of the microprocessors, integrated circuits and memory products. Taking advantage of the available CMOS tools of rapid simulation, testing and fabrication, lower cost, lower power, higher performance imagers can be developed. Photodiodes and phototransistors are common types of detectors used in CMOS imagers. However, they are limited in sensitivity.
Darlington phototransistors have also been recognized as photodetectors. A Darlington phototransistor is an integrated two-stage amplifier device that can obtain a larger current capacity than a typical phototransistor. In the usual Darlington phototransistor, the emitter of a typical phototransistor is connected directly to the base of another transistor that shares a common collector. The collector-emitter current of the one phototransistor is the base current for the second transistor. Thus, the light-induced current is effectively amplified by β2. With known Darlington phototransistors, the second transistor can be driven into saturation with moderate levels of actuating light, which is beneficial over usual phototransistors. However, this is where the benefits of known Darlington phototransistor end.
Therefore, there exists a need in the art to provide a means to produce visible imaging devices that are cheaper, are readily simulated and tested, are lower power, and are more sensitive than existing devices. The present invention addresses such a need.